Step 4: 3rd Sleeve

Now it’s time to trace a sleeve. I forgot to take a picture of this step so I had to improvise. Trace the sleeve of the shirt you’re using adding a 2″ seam allowance all around onto pattern paper or whatever type of large paper you have on hand. Remember that you will need to extend the length of the sleeve to the desired length if using a short sleeve shirt or reduce the length if using a long sleeve shirt as your sleeve pattern. Fold your fabric in half with right sides facing and the wrong side facing you. Place pattern on the fold and cut out the sleeve. Repeat for the second sleeve.

Step 5: 4th

Now take your dress and lay it with right sides facing and pin along the shoulder. Sew the shoulder’s using stretch or small zig-zag stitch and a 1/2″ seam allowance. Finish your seams with a serger, pinking shears, or regular zig-zag stitch.

Step 7: 6th Attaching the Sleeves

Step 8: 7th Finishing the Dress

Now fold the dress with right sides facing. Sew using a 1/2″ seam allowance with a stretch stitch or small zig-zag stitch and finish the seams. Hem the neckline by folding over 1/4″ and then 1/2″. Stitch with a stretch stitch or small zig-zag stitch. Hem the bottom of the dress by folding over 1/2″ and fold over again 1/2″ sew using the stretch or zig-zag stitch.

That dress turned out lovely. I've tried to do things like this in the past and they didn't turn out well. I think I'll try your method with some scrap knit material I have first, to see if it works for me. Did you just tuck the sleeve of the t-shirt under and then fold it in half for the pattern?